In recent years, with improvement of the resolution of an optical sensor in an image pickup apparatus as an optical apparatus, adverse influence of a foreign substance adhering to an optical system during operation of the apparatus, on a picked-up image, has come to be considered increasingly serious. In particular, the resolution of an image pickup device used in a video camera or a still camera has been remarkably improved. For this reason, an image rarely blurs on the surface of the image pickup device, and hence when a foreign substance, such as dust from outside the apparatus and abrasion powder produced on a mechanical sliding surface within the apparatus, adheres to an optical component disposed in the vicinity of the image pickup device, such as an infrared cut filter or an optical low-pass filter, the image of the foreign substance can be taken in a picked-up image.
Further, an image pickup section of a copying machine or a facsimile machine as an optical apparatus causes a line sensor or an original brought close to the line sensor to be scanned to thereby read a plane original. In this case, when a foreign substance adheres to a light ray incidence part via which light enters the line sensor, the image of the foreign substance is taken in a scanned image. In the reader section of a facsimile machine that employs a method of scanning and reading an original or the reader section of a copying machine that employs a method of reading an original during conveyance from an automatic document feeder, i.e. a so-called moving original reading method, an image of a foreign substance is taken as a linear image extending in the original feed direction, which causes serious degradation of image quality.
The image quality can be recovered by manually wiping off the foreign substance. However, a foreign substance that adheres to the light ray incidence part during operation of the apparatus cannot be recognized until after an image has been picked up. If the image is picked up or scanned before the foreign substance is wiped off, an image of the foreign substance is taken in the picked-up image, and hence correction by software is required. In the case of a copying machine, an image is output onto a paper medium simultaneously, and hence it takes a great deal of labor to correct the image.
To solve such a problem, a camera which is provided with a vibration-type dustproof mechanism has been proposed in Japanese Laid-Open Patent Publications (Kokai) No. 2002-204379 and No. 2003-333391. Further, an image reading apparatus has been proposed in Japanese Patent Laid-Open Publications (Kokai) No. 2003-280110 and No. 2004-012474, in which a foreign substance is moved from an image reader section by applying vibration thereto.
FIG. 61 is a view of a conventional dustproof device (foreign substance removing device) disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-204379. This dustproof device has a glass plate 27 as an optical element. A light ray passes through an image-forming light ray passing range 27a within the glass plate 27 to form an image on an image pickup device (not shown). Further, secured to the glass plate 27 are a piezoelectric element A 271, a piezoelectric element B 272, a piezoelectric element C 273, and a piezoelectric element D 274. Between each piezoelectric element and the glass plate 27, there is provided an electrical ground terminal 275.
Each of the piezoelectric elements has sections different in polarizing direction therebetween (each indicated by “+” and “−” in FIG. 61) arranged alternately in the longitudinal direction. The piezoelectric element A 271 and the piezoelectric element C 273 are identical in polarization arrangement in the longitudinal direction. Similarly, the piezoelectric element B 272 and the piezoelectric element D 274 are identical in polarization arrangement in the longitudinal direction. When the length of a pair of sections indicated by “+” and “−” is represented by λ, the position of the section of the piezoelectric element B 272 and that of the piezoelectric element D 274 are displaced by λ/4 in the longitudinal direction with respect to the position of the section of the piezoelectric element A 271 and that of the piezoelectric element C 273.
An oscillator 276 causes a voltage having an in-phase period to be applied to the respective piezoelectric elements A 271 and C 273. On the other hand, a 90° phase shifter 277 causes a voltage having a period shifted in phase by 90° from the phase of the voltage applied from the oscillator 276 to be applied to the piezoelectric elements B 272 and D 274.
However, it is difficult for the conventional foreign substance removing device to generate a traveling wave, which travels on the surface of the glass plate 27, for moving a foreign substance on the glass plate 27. Even if the traveling wave is generated on the surface of the glass plate 27, the traveling wave is reflected from an end of the glass plate 27, and an incident wave and a reflected wave are superposed, which changes the traveling wave into a standing wave. If the traveling wave is changed into the standing wave, the movement at each mass point ceases to be elliptical, which makes it difficult to move the foreign substance in one direction.
Further, when a means for eliminating the reflected wave is employed, it is impossible to utilize a resonance phenomenon caused by the superposition of the incident wave and the reflected wave. For this reason, large amplitude cannot be obtained, and the speed of elliptical vibration is reduced. As a result, speed at which a foreign substance is moved becomes slow, which reduces removing efficiency.